Composite sheet material for brazing

ABSTRACT

The invention relates to a composite sheet material for brazing, the composite sheet material having a structure comprising an aluminium or aluminium alloy substrate on at least one side coupled to a layer comprising a polyolefin/acrylic acid copolymer as a carrier filled with brazing flux material, and optionally also with a metal powder, in an amount sufficient to achieve brazing. The invention further relates to a method of manufacturing composite sheet material for brazing, which method comprises the steps (a) mixing the polyolefin/acrylic acid copolymer with the brazing flux material and/or metal powder, and (b) applying to at least one surface of the metal substrate a mixture of said copolymer filled with the brazing flux material and/or metal powder, in an amount sufficient to achieve subsequent brazing.

FIELD OF THE INVENTION

The invention relates to a composite sheet material for brazing, to theuse of several components in such a composite sheet material, andfurther to a brazed assembly manufactured from such a composite sheetmaterial and to a method a manufacturing such brazed assemblies.

DESCRIPTION OF THE PRIOR ART

A brazing technique which has become widely accepted involves aninert/controlled atmosphere furnace operation (CAB). To destroy andremove the aluminium oxide layer on the aluminium alloy and to protectit during brazing, a flux mixture is often being used to enhance thebrazeability of the brazing alloy prior to brazing. A well known brazingprocess is the NOCOLOC (trade name) brazing process, developed by AlcanInternational Ltd, and for example as disclosed in U.S. Pat. No.3,971,501 and U.S. Pat. No. 3,951,328. This process includes the stepsof forming an assembly, cleaning the surfaces to be brazed to remove oiland grease to eliminate stopoff effects, applying a brazing slurry tothe assembly, blowing off the excess slurry, drying the slurry onto theassembly, and then passing the assembly through a brazing furnace. Theflux does not need to be removed at the end of the brazing cycle. Thebrazing slurry generally includes a brazing alloy and a flux material,but may include additional materials.

A disadvantage of this process are the many processing steps involvedwith the manufacturer of the assembly due to the use of such a brazingslurry.

Another disadvantage encountered with the mentioned brazing process isthat more flux material is often required at the junction between forexample the tubes and headers of a heat exchanger assembly than betweenthe tubes and fins. To overcome this disadvantage, many manufacturerscurrently manually apply a paste-like substance between the tubes andheaders prior to brazing. The paste-like substances provides additionalfiller metal between the tubes and headers and may add additionalmechanical strength to the filet. However, such materials are expensiveand occasionally interfere with the brazing process through the actionof silicon erosion of the underlying aluminium tubes and headers. Alsoother methods of dealing with this disadvantage are known in the art.

A further disadvantage of the mentioned CAB brazing process is that onlyaluminium alloys with a limited magnesium level may be used at standardlevels of this brazing flux application, typically up to about 5 gramflux/m². If the magnesium level in the aluminium alloy is above 0.3weight percent, the flux material gets poisoned due to the formation ofMgO. This disadvantage can only be partly be overcome by applying higherloads of flux material.

A further disadvantage of the mentioned brazing process is that if thefluxing material also contains silicon or zinc an uneven distribution ofthe silicon and zinc after brazing causes preferential corrosion sitesin the assembly.

Many heat exchangers have alternating rows of tubes or plates withconvoluted fins made of aluminium or an aluminium alloy. Many of theseheat exchangers have turbulators disposed within the tubes that requireinternal brazing. Also, CAB furnace brazing suffers from thedisadvantages that the internal tube surfaces and the heat exchangerrequire individual fluxing before assembly and an overall fluxing of thecompleted assembly before brazing. Further, CAB furnace brazing suffersfrom the disadvantage that the individual fluxing of the components ofthe heat exchanger is costly and time consuming.

SUMMARY OF THE INVENTION

An object of this invention is to provide a composite sheet material forbrazing in an inert atmosphere furnace (CAB) operation, as a result ofsaid composite sheet material less processing steps at the side of themanufacturer of the brazed assembly are required.

A further object of this invention is to provide a composite sheetmaterial for brazing in an inert atmosphere furnace (CAB) operation,which avoids the need for individual fluxing of internal and externalsurfaces of the assembly prior to brazing.

A further object of this invention is to provide a composite sheetmaterial which requires less lubrication means, and preferably nolubrication, in a forming operation prior to assembly of the individualcomponents of an assembly for brazing.

A further object of this invention is to provide a method ofmanufacturing composite brazing sheet material in accordance with theinvention.

In accordance with the invention in one aspect there is provided aself-brazing composite sheet material, wherein the composite sheetmaterial having a structure comprising aluminium or aluminium alloysubstrate on at least one side coupled to a layer comprising anolefin-acrylic acid copolymer as a carrier filled with a brazing fluxmaterial in an amount sufficient to achieve brazing.

In an embodiment of the invention the composite sheet material having astructure comprising an aluminium or aluminium alloy substrate on atleast one side coupled to a layer comprising an olefin-acrylic copolymeras a carrier filled with both a brazing flux material and a metalpowder, in an amount sufficient to achieve brazing.

Films made out of this type of copolymer are extensively used for theproduction of packaging material for food. Applying this type ofcopolymer on a metal substrate and using it as a carrier by filling itwith one or more selected from the group comprising brazing fluxmaterial and metal powder, in an amount to achieve brazing, achievesseveral unexpected advantages with respect to brazing technology.

By the invention we can provide a self-brazing composite sheet materialsuitable for use in brazing applications, which overcomes severalprocessing steps at the side of the manufacturer of a brazed assembly,such as individual fluxing of surfaces by applying the brazing flux bymeans of dipping or spraying, drying the applied brazing flux, etc. andall further disadvantages related to these steps.

By the invention we can provide a self-brazing composite sheet materialfor utilisation in brazing operations which no longer requires the stepof individual internal fluxing of surfaces of assemblies prior tobrazing.

The copolymer used is inexpensive and is characterised by excellentadhesion characteristics on a metal substrate, such that the copolymerused as a carrier may be applied on the substrate in the form as coil.Coils of the composite sheet material as such may be supplied to themanufacturer of brazed assemblies, which overcomes all necessaryprocessing steps related to applying and removing of the brazing flux atthis side.

The brazing flux material and/or metal powder are arranged essentiallyhomogeneously throughout the copolymer carrier, where the copolymercarrier has a thickness in the range of up to 150 μm, and preferably upto 50 μm, and more preferably up to 10 μm, and most preferably of notmore than 5 μm, and covers essentially the whole surface area of atleast one side of the metal substrate. The thickness of the filledcopolymer carrier is essentially the same over the whole surface areacovered.

The type of copolymer used as carrier will decompose during heating upfor the brazing cycle and leaves only the brazing materials, namely thefillings of the carrier, on the articles for clean and efficientbrazing. By using a copolymer carrier as indicated a very uniformdistribution of the brazing flux material and/or metal powder isobtained, allowing for a very good brazing process. The amounts ofcarbon residue on the brazed assembly obtained are extremely low and donot affect the final corrosion behaviour of the brazed assembly.

A further advantage of the composite sheet material is that it maycontain dedicated amounts of brazing flux material and/or metal powder.Depending on the circumstances of the case the copolymer as a carriermay be filled with less or even more than standard amount. For examplein the case where the metal substrate is an aluminium alloy containingmore than 0.3 wt. % of Mg more brazing flux material than standardamounts may be added to the carrier in order to overcome thedisadvantage of a higher Mg content as set out above. And furtherbecause the composite sheet material may guarantee a minimum amount ofbrazing flux material and/or metal powder per unit area due to the veryuniform distribution, less filler is required in many applications.

A further advantage of the present invention is that the composite sheetmaterial may be formed in a forming operation prior to assemblingwithout the requirement of a lubricant due to the very good selflubricating nature of the copolymer used. Due to the good adhesion ofthe copolymer to the metal sheet substrate there is no peeling of duringforming operations, not even in extreme situations.

A further advantage of the present invention is that scrap material ofthe composite sheet material may be recycled in a very convenient mannerby using known recycling techniques. Because the type of copolymer usedis can be “burnt off” very easily, for example by using known techniquesfor lacquered UBC's, and leaving very clean metal substrate materialwhich may be readily re-used.

As used herein, the term “olefin” refers to any polymerizable olefin,which may be linear, branched, cyclic, aliphatic, aromatic, substituted,or unsubstituted. More specifically, included in the termolefin-containing polymer are homopolymers of olefin, copolymers ofolefin, copolymers of an olefin and a non-olefinic comonomercopolymerizable with the olefin, such as vinyl monomers, and the like.Specific examples include, ethylene ethyl acrylate copolymer,ethylene/butyl acrylate copolymer, methylene/methacrylic acid copolymer,or ionomer resin. Modified olefin-containing polymer resin is inclusiveof modified polymer prepared by copolymerizing the homopolymer of theolefin or copolymer thereof with an unsaturated carboxylic acid, e.g.,maleic acid, fumaric acid or the like, or a derivative thereof such asthe anhydride, ester or metal salt or the like. It could also beobtained by incorporating into the olefin homopolymer or copolymer, anunsaturated carboxylic acid, e.g., maleic acid, fumaric acid or thelike, or a derivative thereof such as the anhydride, ester or metal saltor the like.

The metal substrate may be in the form of a sheet material, a platematerial, or an extrusion. These aluminium alloys are then used as thestructural member, for which both non-heat treatable as heat treatablealuminium alloys may be applied. Typically material selected from theAluminium Association 3xxx, 5xxx and 6xxx series aluminium alloys areused.

In an embodiment of the composite sheet material in accordance with theinvention the metal substrate is coupled to said filled copolymercarrier via a layer of filler metal. In this case the copolymer carrieris being filled with at least a brazing flux material, and if desiredadditionally with a metal powder to further facilitate brazing.

The filled polymer carrier may be applied very advantageously on variousclad metallurgical products, for example clad products such as disclosedin WO-A-98/24571, WO-A-94/13472, WO-A-96/40458.

In an embodiment of the composite sheet material in accordance with theinvention said copolymer carrier is filled with at least a metal powderselected from the group comprising: aluminium, silicon,aluminium-silicon alloy, zinc, zinc-aluminium alloy, magnesium,aluminium-magnesium alloy, magnesium-zinc alloy, aluminium-zinc alloy,copper, copper alloy, nickel, titanium, silver, indium, lead, germanium,bismuth, strontium, tin, metal powder having a corrosion potentialdifferent from that of the underlying metal substrate, metal powderhaving a corrosion potential lower than that of the underlying metalsubstrate.

A wide variety of metal powder may be added in said copolymer carrier independence of the metal sheet substrate used, and when used also fromthe type of brazing flux. Metal powder particles range in size from upto 200 μm, but the preferred range is up to 60 μm, and more preferablyin a range of up to 10 μm, in dependence of the thickness of thecopolymer layer applied and for reasons of ease of processing.

In case where the metal substrate is made of aluminium or an aluminiumalloy, the carrier may advantageously be filled with at least variousmetal powders. For the purpose of this application both silicon andgermanium are considered to be metals.

An Al—Si powder or a suitable mixture of Al powder and Si powder maygenerally be used. The former is more preferable in order to ensure abetter flowability of the brazing agent when the aluminium articles oraluminium alloy articles are brazed. A preferable content by weight ofSi in the Al—Si powder is 3 to 15%, or more preferably 6 to 12% so thatan appropriate liquidus line temperature is ensured to afford anexcellent brazing. Alternatively, they may be added in the form of aMg—Zn alloy powder or the like, or an Al—Si series alloy such asAl—Si—Mg alloy and Al—Si—Zn alloy. The addition of Sn or Cu powder tothe metal powder or metal powder/flux material mixture may enhance forexample corrosion resistance.

Addition of magnesium (Mg) will improve the mechanical strength of thebrazed joint. Addition of indium (In) and/or zinc (Zn) and/orzinc-aluminium alloy will increase corrosion resistance, and theaddition of bismuth (Bi) and/or strontium (Sr) will improve thebrazeability of the articles, and further the addition of berryllium(Be) will be effect to more perfectly braze Mg-containing aluminiumalloy articles.

In an embodiment the carrier is filled at least with a suitable brazingalloy powder such that the composite material does not need theadditional layer of filler metal or brazing metal on at least one sideof the metal substrate, which are most frequently used when brazingaluminium or aluminium alloys.

In an embodiment of the composite sheet material in accordance with theinvention the polyolefin comprises ethylene. These copolymers provide anexcellent adhesion on metal substrates, are inexpensive and readilycommercially available. These copolymers leave almost no carbon residueon the final brazed assembly. Due to the excellent adhesion of thecopolymer to the metal substrate there is no peeling of during formingoperations, not even in extreme situations.

Ethylene/methacrylic acid copolymer, ethylene/acrylic acid copolymer andtheir metal-salt neutralized counterparts (e.g. ionomer resins) havebeen well known for several years to be the best of the metal-adheringpolyolefin materials. Typical heat sealing materials are branched lowdensity polyethylene (LDPE), ionomers such as the Surlyn (trade name)brand sold by DuPont Company, ethylene/methacrylic acid copolymers suchas Nucrel (trade name) sold by DuPont Company, ethylene/acrylic acidcopolymers such as Primacor (trade name) sold by Dow Chemical Companyand EVA copolymers.

Although the invention works for a wide variety of densities of thepolyethylene, low density polyethylene (LDPE) is preferred, since thesepolymers decompose at relatively low temperature. In a more preferredembodiment the VLDPE or even ULDPE are used, since these are even easierto remove and decompose at lower temperatures. The lower thedecomposition temperature of the applied copolymer, the lower thebrazing temperature may be chosen in dependence of the brazing fillerand/or brazing flux material used.

The copolymer carrier may be filled with various kind of brazing fluxmaterials depending on the type of metal substrate. In the embodiment ofan aluminium or aluminium alloy substrate suitable brazing fluxmaterials may be a fluoride flux, a chloride flux or the like. Thesuitable fluoride fluxes may include the compounds having a molecularformula K_(a)AlF_(a+3) (‘a’ being an integer equal to or greater than1), such as KAlF₄, K₂AlF₅ and K₃AlF₆. The fluoride fluxes furtherinclude: a simple mixture of KF and AlF₃; an eutectic mixture thereof;and a certain complex such as potassium fluoroaluminate. Any one ofthese fluxes may be selected, though two or more of them may be added incombination. Other suitable fluxes may contain potassium fluoroaluminatemixed with one or more of cesium chloride, rubidium chloride, lithiumfluoride, cesium fluoride and other halide salts to reduce the meltingpoint of the flux. Some preferred examples of chloride fluxes are thosewhich contain ammonium chloride, BaCl₂, NaCl, KCl and/or ZnCl₂ as theirmain components. Either any one of them or any mixture thereof may beadded to the carrier to produce the brazing flux material. The brazingflux material is also preferably used in a powder consistency, and inthe embodiment of the combination with metal powder the brazing fluxmaterial powder are usually present in a metal/flux weight ratio rangeof 1:10 to 10:1.

The brazing flux material has preferably an average size of less than 5micron, and more preferably less than 2 micron. Utilising suchrelatively small brazing flux material results in a very efficient CABbrazing operation, whereas in the forming operation of the compositesheet material prior to assembly before brazing does not result in anynoticeable wear in the tooling. Further by using such relatively smallbrazing flux material in the copolymer carrier, the self lubricationproperties of the copolymer carrier in a forming operation can be usedoptimally. It will be understood by those skilled in the art that thesize of the brazing flux particles should be smaller than the thicknessof the copolymer layer.

In accordance with the invention it has been found that good brazing ofthe resultant assembly can be achieved utilising lower amounts ofbrazing flux material than standard per side of the composite sheetmaterial. Brazing flux material applied per side of the composite sheetmaterial preferably does not exceed 5 gram/m², and preferably is lessthan 3 gram/m² to achieve brazing.

At present the most widely used brazing flux material is the NOCOLOK(trade name) material. An advantage of this brazing flux is that it isstable at room temperature in a normal atmosphere, because it isessentially nonhygroscopic. This means that the composite material inaccordance with the invention may be stored for a long period of timewithout any deterioration of the carrier and its fillings. However, inthe case that the carrier is filled with a material which is susceptiblefor atmospheric influences, than on the filled copolymer a further(co)polymer layer may be adhered to seal off the carrier from theatmosphere. There is no need for a metallic covering layer forprotecting subsequent processing tools from damage by the powder in thecopolymer carrier.

The invention also consists in the use of an polyolefin/acrylic acidcopolymer in a composite material as set out above.

In a further aspect the invention consists in the use of apolyolefin/acrylic acid copolymer filled with one or more selected fromthe group comprising brazing flux material and metal powder, in anamount to achieve brazing, for use in a composite sheet material as setout above. In a more preferred embodiment for the metal powder a metalis being selected from the group comprising: aluminium, silicon,aluminium-silicon alloy, zinc, zinc-aluminium alloy, magnesium,aluminium-magnesium alloy, magnesium-zinc alloy, aluminium-zinc alloy,copper, copper alloy, nickel, titanium, silver, indium, lead, germanium,bismuth, strontium, tin, metal powder having a corrosion potentialdifferent from that of the underlying metal substrate, metal powderhaving a corrosion potential lower than that of the underlying metalsubstrate.

In another aspect of the invention there is provided in a method ofmanufacturing a composite sheet material as set out above, wherein thecopolymer is firstly mixed at a temperature in the range of up to thenormal processing temperature, e.g. by means of extrusion, of thecopolymer used with the brazing flux material and/or metal powder, andthen applied onto the aluminium or aluminium alloy substrate, being inthe form of a sheet material or an extrusion. Where the method is usedon an industrial scale, the mixture may be applied onto the metalsubstrate by means of techniques such as co-extrusion, spraying, thermalspraying, lamination and calandering, and roll coating. In the resultantcomposite sheet material the brazing flux material and/or metal powderare arranged essentially homogeneously throughout the copolymer carrier,where the copolymer carrier has a suitable thickness in the range of upto 150 micron, and preferably up to 50 micron, and more preferably up to10 micron, and most preferably of not more than 5 micron, and coversessentially the whole surface area of at least one side of the metalsubstrate. The thickness of the filled copolymer carrier is essentiallythe same over the whole surface area covered.

In accordance with the invention it has been found that the mixing ofthe copolymer with the brazing flux material is preferably carried outin the absence of water as a solvent of the copolymer, and morepreferably in the absence of any solvent for the copolymer. Thisachieves the effect that less processing step are required for themethod of manufacturing the composite sheet material of the invention,e.g. the step of drying the applied filled carrier has been overcome.Furthermore, it achieves the effect that the subsequent CAB brazingoperation can be carried out with a much higher efficiency, inparticular since it has been found from experimental work thatcopolymers of the type set out above using water as a solvent as verydifficult to use of subsequent brazing operations. The reasons behindthis is not yet fully understood.

Where the metal substrate is in the form of a sheet material, thecomposite sheet material may advantageously be coiled and subsequentlytransported to a manufacturer of brazed assemblies, which does no longerhave to apply the brazing flux material himself. Here the compositesheet material may be uncoiled, sized and cut, formed where necessary,assembled and heated to remove the copolymer carrier and subsequentlyheated to a temperature above the brazing alloy melting point forjoining the surfaces of the assembly by means of brazing, and thenallowing the brazed assembly to cool.

Where possible the heating of the assembly to remove the copolymercarrier in order to expose its fillings to the metal substrate and theheating for the brazing cycle advantageously may be combined. Theself-brazing composite sheet material in accordance with the inventionmay be formed without the requirement of a lubricant due to the selflubricating nature of the copolymer used. And further the need forapplying the brazing flux by means of dipping or spraying, drying theapplied brazing flux, etc. and all further disadvantages related tothese steps are overcome.

In another aspect the invention relates to a brazed, assembly comprisingat least one component made of the composite sheet material inaccordance with this invention, and which brazed assembly has beenbrazed preferably in a CAB brazing operation.

In a further aspect the invention relates to a brazed assembly which hasat least one internal brazed surface. In the way it is achieved that theassembly does not need to be fluxed separately on the internal surfaceafter assembling of the assembly prior to CAB brazing.

In a further aspect of the invention it related to a method ofmanufacturing a brazed assembly using the composite sheet material asset out above, comprising the subsequent steps of:

(a) providing at least one substrate material of aluminium or analuminium alloy;

(b) coupling on at least one side of the substrate a filledpolyolefin/acrylic acid copolymer carrier comprising brazing fluxmaterial, optionally in combination with a metal powder, in an amountsufficient to achieve brazing, as set out above;

(c) forming parts of which at least one is made of a composite sheet forbrazing having a structure comprising an aluminium or aluminium alloysubstrate on at least one side coupled to a layer comprising saidcopolymer as a carrier filed with the brazing flux material, optionallyin combination with a metal powder, in an amount sufficient to achievebrazing;

(d) assembling the parts into the assembly;

(e) brazing the assembly in an CAB brazing operation to achieve brazing;

(f) cooling the brazed assembly to below 100° C. with a cooling rate ofat least 20° C./min.

This achieves the effect providing a method for manufacturing a brazedassembly, in which method overcomes several processing steps at the sideof the manufacturer of a brazed assembly, such as individual fluxing ofinternal and external surfaces by applying the brazing flux by means ofdipping or spraying, drying the applied brazing flux, etc. and allfurther disadvantages related to these steps. Further advantages of thismethod have been set out above.

It should be mentioned here that from U.S. Pat. No. 5,251,374 a methodis known for assembling a brazed heat exchanger unit. In the knownmethod during assembling of the various parts very locally andaccurately on specific surfaces a flux-brazing composition may beemployed, so as to facilitate the brazing of internal and externaljoints of the heat exchanger. The flux-brazing composition consists of aconventional flux, such as potassium tetrafluoroaluminate particles, analuminium-silicon powder, a metal whose electrode potential is less thanthat of the aluminium alloy from which the tubes and headers are formed,and a binder. The suggested binder is made of a hydroxypropyl cellulose.In an alternative embodiment the flux-brazing composition is suspendedin a liquid carrier, such as a glycerin-ethylene glycol carrier system,to permit the flux-brazing composition to be applied as a slurry.

It should be mentioned here than from U.S. Pat. No. 5,360,158 aflux-coated alloy member for selectively placing a flux compound betweenan aluminium containing alloy and a joint of an assembly which is to bejoined is known. The flux-coated alloy member comprises a band memberformed from the alloy and a flux coating adhered to substantially allexternal surfaces of the band member, the flux coating comprising theflux compound dispersed in an adhesive binder, the adhesive binder beingselected from the group consisting of (a) natural resins selected fromthe group of water-white resin and shellac, and (b) water-soluble epoxyresins, and whereby the flux-coated alloy member enables the fluxcompound to be selectively placed at the joint of the assembly so as tosubstantially eliminate the presence of excess flux compound at thejoint.

Further it should be mentioned here that from WO-A-98/50197 a method isknown comprising coating an aluminium formed material to be jointed witha flux composition comprising 0.5 to 25 parts by weight of a polymericcompound having a number average molecular weight of 50,000 to 5,000,000and comprising repeating alkylene oxide units, 5 to 30 parts by weightof a fluoride flux, and water added as a liquid carrier in such anamount as will provide a total amount of the composition of 100 parts byweight, and heating the coated area to remove water, heating the coatedarea to decompose and remove the polymeric compound, and then conductingheating for brazing.

EXAMPLES

The invention will now be explained by several non-limitative examples.

Example 1

On a laboratory scale of testing the burn out characteristics of severalpolymers have been measured using Thermal Gravimectric Analysis (TGA).This TGA technique measures weight decrease versus temperature. Thefollowing data have been determined: (a) the temperature where theweight decrease becomes zero, and (b) the residual weight at thistemperature. The results for several polymer tested are listed in Table1.

TABLE 1 Residual Temperature weight Polymer [° C.] [%] Polyethyleneterephthalate (PET) 534 8.6 Polyvinylacetate (PVA) 534 8.9 Polyethyleneacid copolymer (PEA) 500  0.02 Polyethylene maleic acid modified (PE)500  0.02 Polyethylenevinylacetate copolymer (PEVA) 507 0.2Polyvinylbutyrate (PVB) 496 2.1

From the results of Table 1 it can be seen that the copolymers PEA, PEVAand PE tested have good burn out properties, and of which PEA and PEshow excellent burn out properties. Further several grades of PEA havebeen tested and all showed excellent burn out properties.

Example 2

On a laboratory scale of testing 183 gram of commercial available Nucrel(trade name) 1214 with 165 gram of NOCOLOK brazing flux material(particle size between 0.5 and 20 μm, having d10=0.76 μm and d90=4.99μm) have been mixed for 20 minutes at a temperature of 210° C. Brazingsheet material consisting of 0.4 mm thick core material of AA3003-seriesalloy with a cladding of 10% of the core thickness of AA4343-seriesmaterial has been used. The sheets have been cleaned with ethanol. Themixed copolymer with the flux material has been applied between twosheets of brazing sheet material followed by pressing for 1 minute witha pressure of 100 bar at a temperature of 250° C. After pressing the twosheets are immediately separated and allowed to cool to roomtemperature, and leaving a filled copolymer with a thickness of 5 μm. Byrepeating this procedure by putting a clean brazing sheet material onthe brazing sheet with the 5 μm thick carrier, the resultant carrierthickness is 2.5 μm. Subsequently the brazing sheet material with thefilled copolymer carrier were again placed in the press with thetemperatures of the plates set at 160° C. and a sheet of Teflon (tradename) on the carrier coated side. Pressing took place at 250 bar for 30seconds, which operation was carrier out to smoothen the surface of thecopolymer flux.

The brazing sheet material with the filled carrier of 5 and 2.5 μmthickness have been brazed for 1 min. at 585° C. under controlled CABconditions using nitrogen flow. The brazed configurations consisted of abrazing sheet material with dimensions 25×25 mm on top on which aV-shaped bended AA1000-series aluminium strip with thickness 1 mm hasbeen placed; the V-shaped angle is 45°. The configuration applied wasidentical as demonstrated in FIG. 3 in the SAE-980052 paper entitled“Stability of R124a in the presence of Nocolok flux residues” by C.Meurer et al. The resultant brazed joint was excellent, the fillet sizewas fine, and the fillet was smooth without stitches, and thewettability of the filler in the corner of the V-shaped bend showed goodcapillary raise.

Example 3

Analogue to Example 2 in this experiment 135 gram of Nucrel (tradename)-1214, 125 gram of NOCOLOC brazing flux material (the same as withExample 2), and 81 gram of silicon powder (purity grade larger than 99%and smaller than 325 mesh) have been mixed and applied on anAA3003-series core material without a cladding material. The thicknessof the resultant filed carrier was 50 μm.

The brazing sheet material with the filled carrier of 50 μm thicknesshave been brazed for 1 min. at 590° C. under controlled CAB conditionsusing nitrogen flow. The brazed configurations consisted of a brazingsheet material with dimensions 25×25 mm on top on which a V-shaped bendAA1000-series aluminium strip with thickness 1 mm has been placed; theV-shaped angle is 45°. The configuration applied was identical asdemonstrated in FIG. 3 in the SAE-980052 paper entitled “Stability ofR124a in the presence of Nocolok flux residues” by C. Meurer et al. Theresultant brazed joint was excellent, the fillet size was fine, and thefillet was smooth without stitches, and the wettability of the filler inthe corner of the V-shaped bend showed good capillary raise.

Example 4

Composite brazing sheet material in accordance with the inventioncomprising a filed carrier of 20 μm thickness on both sides of the sheetmaterial has been subjected to Erichsen tests. The parameter were: 138mm blank diameter, 0.5 mm thickness of the blank, blankholder force 5-8kN. This was found that a deep-drawing-ratio of 1.84 no delamination ofthe copolymer occurred, nor on the inside or the outside of thedeep-drawn cups.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade without departing from the spirit or scope of the invention as setforth by the claims appended hereto.

What is claimed is:
 1. A coiled composite sheet material for brazing,the composite sheet material having a structure comprising a metalsubstrate, selected from the group consisting of an aluminium substrateand an aluminium alloy substrate on at least one side coupled to acopolymer carrier layer having a thickness of at most 150 μm andcomprising copolymer of ethylene and acrylic acid as a carrier filledwith a brazing flux material, said brazing flux material comprising atleast one member of the group consisting of a fluoride flux and achloride flux in an amount sufficient to achieve brazing, and thebrazing flux material has an average particle size dimension of lessthan 5 μm and the amount of brazing flux material per side of thecomposite sheet material is less than 5 gram/m² and is arrangedsubstantially homogeneously throughout the copolymer carrier layer andthe thickness of the filled copolymer carrier layer is substantially thesame over the whole surface area covered.
 2. A composite sheet materialin accordance with claim 1, wherein the metal substrate is coupled tothe filled copolymer carrier via a layer of filler metal.
 3. A compositesheet material in accordance with claim 1, wherein the copolymer carrierlayer has a thickness of at most 50 μm, and covers substantially thewhole surface area of at least one side of the aluminium or aluminiumalloy substrate.
 4. A composite sheet material in accordance with claim1, wherein the brazing flux material in combination with metal powder,are arranged substantially homogeneously throughout the copolymercarrier layer.
 5. A composite sheet material in accordance with claim 1,wherein the brazing flux material has an average particle size dimensionof less than 2 μm.
 6. A composite sheet material in accordance withclaim 1, wherein the amount of brazing flux material per side of thecomposite sheet material is less than 3 gram/m².
 7. A composite sheetmaterial in accordance with claim 1, wherein at least one said copolymercarrier layer is filled with both said brazing flux material and metalpowder.
 8. A composite sheet material in accordance with claim 1,wherein the copolymer carrier layer has a thickness of at most 10 μm,and covers substantially the whole surface area of at least one side ofthe aluminium or aluminium alloy substrate.
 9. A composite sheetmaterial in accordance with claim 1, wherein the metal substratecomprises a member of the group consisting of Aluminium Association3xxx, 5xxx, and 6xxx series aluminium alloys.
 10. A composite sheetmaterial in accordance with claim 1, wherein the copolymer carrier layercomprises said brazing flux material and a metal powder having acorrosion potential lower than that of the underlying metal substrate.11. A composite sheet material in accordance with claim 1, wherein thecopolymer carrier layer has a thickness of at most 5 μm, and coverssubstantially the whole surface area of at least one side of thealuminium or aluminium alloy substrate.
 12. A composite sheet materialfor brazing according to claim 1, wherein the copolymer carrier layercomprises the copolymer as the carrier filled with both the brazing fluxmaterial and a metal powder, in an amount sufficient to achieve brazing.13. A composite sheet material in accordance with claim 12, wherein themetal powder particles range in size up to 60 μm.
 14. A composite sheetmaterial in accordance with claim 12, wherein the metal powder particlesrange in size up to 10 μm.
 15. A composite sheet material in accordancewith claim 1, wherein the copolymer carrier layer is at least filledwith the brazing flux material and a metal powder selected from thegroup consisting of aluminium, silicon, aluminium-silicon alloy, zinc,zinc-aluminium alloy, magnesium, aluminium-magnesium alloy,magnesium-zinc alloy, aluminium-zinc alloy, copper, copper alloy,nickel, titanium, silver, indium, lead, germanium, bismuth, strontium,and tin.
 16. A method, of manufacturing composite sheet material forbrazing of claim 1, which comprises: (a) mixing the copolymer ofethylene and acrylic acid with the brazing flux material in the absenceof water as a solvent for the copolymer of ethylene and acrylic acid,and (b) applying to at least one side of the metal substrate a mixtureof the copolymer filled with the brazing flux material, in an amountsufficient to achieve subsequent brazing.
 17. A method of manufacturinga composite sheet material for brazing of claim 12, which comprises: a.mixing the copolymer of ethylene and acrylic acid with the brazing fluxmaterial and metal powder in the absence of water as a solvent for thecopolymer of ethylene and acrylic acid, and b. applying to at least oneside of the metal substrate a mixture of the copolymer of ethylene andacrylic acid filled with the brazing flux material and metal powder, inan amount sufficient to achieve subsequent brazing.
 18. A method of useof a sheet of a composite sheet material as defined in claim 1,comprising brazing the sheet to another component of an assembly.
 19. Amethod of manufacturing a brazed assembly using the composite sheetmaterial of claim 1, comprising the steps of: forming parts of which atleast one is made of the composite sheet material; assembling the partsinto the assembly; brazing the assembly in an CAB brazing operation toachieve brazing; and cooling the brazed assembly to below 100° C. with acooling rate of at least 20° C./min.
 20. A method of use of a sheet of acomposite sheet material as defined in claim 15, comprising brazing thesheet to another component of an assembly.
 21. A method of use of asheet of a composite sheet material as defined in claim 15, comprisingbrazing the sheet to another component of an assembly using a controlledatmosphere (CAB) process.